1. Field of the Invention
The present invention relates to non-halogen multilayer insulated wires that are superior in abrasion resistance, hydrolysis resistance, flame retardance, heat resistance and electrical properties (direct current stability) and exhibit low smoke emission and low toxicity, and particularly to a non-halogen multilayer insulated wire complying with European standards (EN standards).
2. Description of the Related Art
Transfer wires and cables used for, for example, railway vehicles and cranes use a halogen-including rubber mixture balanced in terms of oil-fuel resistance, properties at low temperatures, flame retardance, flexibility and cost, such as chloroprene rubber mixture, chlorosulfonyl polyethylene mixture, chlorinated polyethylene mixture, and fluorocarbon rubber mixture.
However, these materials including a large amount of halogen and may release a large amount of toxic, harmful gas, depending on burning conditions, when burning. Accordingly, wires and cables having sheaths that are made of halogen-free material (non-halogen material) not including any halogen are increasingly used from the viewpoint of reducing environmental impact and fire safety.
On the other hand, in Europe, where rail vehicle networks are developed, the regional unified standards called EN standards (European standards) are widely adopted. The EN standards require that halogen-free materials used for wires and cables for railway vehicles be resistant to abrasion, hydrolysis and heat, and exhibit flame retardance, low smoke emission and satisfactory electrical properties (direct current stability) because a defective wire or cable may result in a major accident.
Japanese Unexamined Patent Application Publication No. 2011-228189 is intended to satisfy the requirements of the EN standards. This patent document discloses a multilayer wire including a conductor, an inner layer made of a polyester resin composition including a polyester resin (such as polybutylene terephthalate or polybutylene naphthalate), a polyester block copolymer, a hydrolysis inhibitor and a calcined clay, and an outer layer made of a polyester resin composition including a polyester resin (such as polybutylene terephthalate or polybutylene naphthalate), a polyester block copolymer, a hydrolysis inhibitor, a calcined clay and magnesium hydroxide. The conductor is covered with the inner and outer layers. Each of the polyester block copolymers includes: (a) 20% to 70% by mass of a hard segment mainly including polybutylene terephthalate including 60% by mole or more of terephthalic acid relative to the total number of moles of the dicarboxylic acid component, and (b) 30% to 80% by mass of a soft segment including a polyester including 90% to 99% by mole of an aromatic dicarboxylic acid as the acid component, 1% to 10% by mole of linear aliphatic dicarboxylic acid having a carbon number of 6 to 12, and a linear diol having a carbon number of 6 to 12 as the diol component. The melting point (T) of the polyester block copolymer satisfies the relationship: TO−5>T>TO−60, wherein TO represents the melting point of the polymer including the components of the hard segment.
The EN standards require that the wires and cables one less toxic, in addition to the above characteristics. However, known techniques, including the above cited Japanese Unexamined Patent Application Publication No. 2011-228189, have not been able to produce a wire or cable satisfying all the specifications of the EN standards.